Method and device for the production of a hydraulic binding agent

ABSTRACT

The invention relates to a method and to apparatus for the production of a hydraulic binding agent from a plurality of raw material components ( 12   a  to  12   e ), wherein the raw material components are ground to a raw meal, the raw meal is burned to clinker in a combustion plant ( 2 ) and finally the clinker is ground together with further inter-grinding materials. Moreover, the mineralogical and/or chemical composition of the raw meal and/or the clinker is analysed, at least two separate raw meal silos/clinker silos ( 4   a  to  4   h,    5   a  to  5   g ) are provided in each case for the raw meal and/or the clinker and are filled with raw meal/clinker of different mineralogical and/or chemical composition. Furthermore the composition of the raw meal to be burned and/or of the clinker to be ground is fixed by controlled extraction as a function of the analysed composition of the raw meal/clinker from one or a plurality of raw meal silos/clinker silos.

The invention relates to a method and apparatus for the production of ahydraulic binding agent from a plurality of raw material components,wherein the raw material components are ground to a raw meal, the rawmeal is burned to clinker in a combustion plant and finally the clinkeris ground together with further inter-grinding materials.

In the production of cement clinker, in the process section ofpreparation of the raw material the principal oxides CaO, Al₂O₃, Fe₂O₃und SiO₂ from materials such as for example limestone, marl, clay,bauxite, iron ore, sand, etc. are mixed in such a way that the ratios ofthe CaO to the other three oxides, of the SiO₂ to the alumina and ironoxide as well as of the alumina to the iron oxide lie within a desiredvalue range. These three ratios, also referred to as raw materialmodules, are, in addition to the further subordinate characteristicquantities for the subsidiary components, the most importantcharacteristic quantities of quality of the raw meal, since by means ofthese the mineralogical main phases of the cement clinker C3S, C2S, C3Aand C4AF (in cement notation) and thus the properties of the cementclinker can be set. However, alkalis, sulphates, halogens and furtherelements contained in smaller mass fractions are also of considerableimportance for the properties of the clinker minerals.

In addition to the necessary fine grinding for the clinker burningprocess, the preparation of the raw material has to ensure the dryingand homogeneity of the modules—expressed as a standard deviation fromthe desired mean values.

Nowadays the cement clinker is usually burned in a clinker productionline comprising a preheater, calciner, rotary kiln and clinker cooler.In the cement grinding installation the cement clinker is the ground byaddition of a sulphate admixture as setting regulator and furtherinter-grinding materials, such as for example granulated blast furnaceslag, fly ash, pozzolanas, limestone and burnt oil shale, to producedifferent cements with their respective properties. The said processsections of preparation of the raw material, clinker burning and cementgrinding are each separated by stores. These stores provide a stock ofmaterial in order to break the link between the availability of a partof the installation and the readiness for operation of the other partsof the installation. Furthermore, especially between preparation of theraw material and clinker burning the fluctuations in the characteristicquantities of quality are damped by the silo in order to achieve themost constant possible quality of the raw meal. The characteristicquantities of quality of the individual process sections are checked byperiodic sampling after the individual process sections and the valuesdetermined are used within the context of regulation for changes tocontrol variables upstream in the material.

This procedure is associated with the following technical and economicdisadvantages:

The characteristic quantities of quality which are most important forthe cement end product, but not the only ones, are compression strengthas a function of time, beginning and end of setting, water requirementto standard stiffness, sulphate resistance, etc. Some of thesecharacteristic quantities can still be influenced by the last processsection of cement grinding, since significant properties have alreadybeen influenced or adjusted in the preceding process sections. Thus theraw material modules influence the mass ratio of the clinker phasesproduced, which in turn have a primary influence on the properties ofthe cement. However, the prior calculation of the clinker phases, e.g.by the Bogue method, is only sufficiently reliable when the subsidiaryand trace elements are present in small quantities. Especially in theeconomically important use of waste-derived fuels or waste materialsfrom other industries—in the context of a composite process—theprediction of clinker phases and thus cement properties is not possiblewith sufficient precision. Furthermore the clinker phases are notdistributed homogeneously over the clinker grain size distribution.

A further disadvantage results from the size of the stores which isfrequently fixed by considerations of availability and implies a highdead time and thus leads to a low flexibility in the adaptation of theproduct quality to changed production conditions. In raw material silos,which when completely full hold a stock for e.g. 1 to 2 days, aneconomically advantageous change of fuel cannot take place in a shorttime without lasting change to the product quality.

A method and apparatus is known from WO-A-02/083279 in which a pluralityof silos are provided for storage of the raw meal, wherein theindividual silos are filled one after the other with the raw meal andthe raw meal is extracted simultaneously from a plurality of silos. Inthis way a high rate of homogenisation is achieved, whereby a constantand stable combustion process is ensured. However, this method also doesnot allow a change of fuel in a short time without lasting change to theproduct quality.

The object of the invention, therefore, is to propose a method andapparatus by which the long dead times resulting from the sizes of thestores are avoided and additionally it is possible to influence thecharacteristic quantities of quality downstream with respect to thematerial flow direction of the process sections set out above.

This object is achieved according to the invention by the features ofClaims 1 and 8 respectively.

In the method according to the invention for the production of ahydraulic binding agent from a plurality of raw material components theraw material components are ground to a raw meal, the raw meal is burnedto clinker in a combustion plant and finally the clinker is groundtogether with further inter-grinding materials. Furthermore themineralogical and/or chemical composition of the raw meal and/or theclinker is analysed, wherein at least two separate raw mealsilos/clinker silos are provided in each case for the raw meal and/orthe clinker and are filled with raw meal/clinker of differentmineralogical and/or chemical composition, and wherein the compositionof the raw meal to be burned and/or of the clinker to be ground is fixedby controlled extraction as a function of the analysed composition ofthe raw meal/clinker from one or a plurality of raw meal silos/clinkersilos. In this way a targeted regulation of the product quality takesplace.

The apparatus according to the invention for the production of ahydraulic binding agent from a plurality of raw material componentsbasically comprises a grinding apparatus for grinding of the rawmaterial components to raw meal, a combustion plant for burning of theraw meal to clinker and a cement grinding installation for grinding ofthe clinker, wherein at least one analysing means is provided foranalysis of the mineralogical and/or chemical composition of the rawmeal and/or of the clinker. Furthermore the apparatus has a raw mealsilo installation and/or a clinker silo installation, wherein at leasttwo separate raw meal silos/clinker silos are provided in each case forthe raw meal and/or the clinker. By way of a control device the raw mealsilos/clinker silos are filled as a function of the mineralogical and/orchemical composition of the raw meal/clinker. Furthermore, by way of thecontrol device the composition of the raw meal to be burned and/or ofthe clinker to be ground is fixed by controlled extraction as a functionof the analysed composition of the raw meauclinker from one or aplurality of raw meal silos/clinker silos.

In the method known from WO-A-02/083279 fluctuations in the raw mealcomposition can only be compensated for by a mean value(homogenisation), whereas according to the invention the composition ofthe raw meal is only fixed after the grinding operation as a function ofthe analysd composition of the ground raw material components bytargeted extraction from the raw meal silos.

Further embodiments of the invention are the subject matter of thesubordinate claims.

According to a preferred embodiment the mineralogical and/or chemicalcomposition of the clinker is determined and used for control of theextraction of the raw meal from the raw meal silos.

Acording to a further embodiment individual raw material components areat least partially ground separately and stored in separate raw mealsilos.

Furthermore, the filling of the clinker silos and the extraction of theclinker from one or a plurality of clinker silos are regulated as afunction of the desired mineralogical and/or chemical composition of thecement to be created.

For determination of the mineralogical and/or chemical composition ofthe raw meal/clinker samples which are fractionated according to grainsize and/or density samples can be taken and analysed. It is also anobject of the present invention to carry out the filling of the raw mealsilos/clinker silos by fractionation by means of screening or siftingaccording to grain size and/or density.

For the storage of materials, the various silos can be specificallyfilled with materials with different characteristic quantities ofquality. The filling can take place either on the basis of a simpledirection of the material stream to a silo by way of a switch or also onthe basis of a classification according to grain sizes or densities byscreening or sifting. In this way it is possible to take into account ofthe fact that cement clinker has a concentration of the clinker phaseswhich varies according to grain size.

The chemical/mineralogical sample analysis systems are disposed beforethe silos and after the subsequent process section and on the basis ofthe measured values determined in periodic intervals before the fillingallow the decision concerning the silo(s) in which the sample materialis stored and on the basis of the characteristic quantities of qualityachieved after the subsequent process section allow the decisionconcerning the quantities of material to be extracted from theindividual silos. The results of the analysis in connection with fillingtime, filling quantity and filling location are stored temporarily forfurther regulation.

According to the prior art the method of X-ray diffractometry withquantitative evaluation by the Rietveld method is usually used for theclinker phase determination and an X-ray fluorescence method is used forthe determination of the raw material modules. However, otheralternative or supplementary methods are also possible.

In this case the individual silos or silo compartments, in particular onthe raw meal side, are advantageously constructed in such a way that amass flow is ensured. As a result horizontal layers are produced in thesilo compartments with known characteristics of quality. By theseparation of the storage according to characteristic quantities ofquality and the controlled emptying of each individual compartment it ispossible to regulate the characteristic quantities of quality in atargeted manner in the subsequent process.

The clinker silo can also be formed simply by a stockpile separated bywalls or partitions.

The sample analysis systems generally comprise the components ofsampling, sample preparation and measurement as well as a control meansand software for the evaluation and analysis of measurment data.Moreover the sampling can also comprise additional fractionating devicesby denbsity and/or grain size.

If such a system is used not only for the raw meal between preparationof the raw material and clinker burning but also for the clinker betweenclinker burning and cement grinding, then the emptying of the individualraw meal silos can be regulated using the characteristic quantities ofquality determined by the clinker sample analysis system. In this wayunpredictable changes can be stabilised by secondary fuels or secondaryraw materials—e.g. brown coal fly ash, tyres, domestic refuse—on theclinker phases.

In combined grinding an unwanted chemical composition separatedaccording to grain sizes is frequently observed. With the invention itis also advantgeously possible to produce individual raw meal componentsby separate grinding and storage. The bringing together of separatelyground raw meal components makes possible an improved control of thechemical composition irrrespective of the grindability. Also correctivecomponents which are distinguished by a high concentration of aprincipal oxide or of a subsidiary component, can be produced and storedseparately for later corrections and if need be can be added to themixture with short dead times.

Furthermore, the problems which exist when the proportioning of a rawmaterial component fails can be avoided. In this case it is frequentlyno longer possible to maintain the required value range of thecharacteristic quantities of quality and no sufficient possibilities forcorrection exist in the further material flow. In this case the separatestorage of individual components provides a time buffer in order tocorrect the errors in the recipe. With the present-day state of the art,in particular in the case of materials which are difficult to handle,such as for example strongly adhesive clay or returned filter dust, thisleads to problems of availability of the plant, as the plant has to bestopped and the disruption has to be eliminated.

Further embodiments and advantages of the invention are explained ingreater detail below with reference to the description and the drawings.

In the drawings:

FIG. 1 shows a schematic overview of a plant for the production of ahydraulic binding agent and

FIG. 2 shows a schematic view of a raw meal silo instalation/clinkersilo installation.

The overview shown in FIG. 1 shows a plant for the production of ahydraulic binding agent, in particular cement and cement clinker.

It comprises the process sections for preparation of the raw material 1,clinker burning 2 and cement grinding 3. A raw meal silo installation 4or a clinker silo installation 5 respectively is provided between theprocess sections. The finished ground cement arrives at a cement silo 6into which it can be filled for further transport.

The raw material components 12 a to 12 e, such as lime, clay, iron ore,etc. which are necessary for the cement production are at leastpartially pre-comminuted in crushers 10 and then proceed via storagefacilities into separate storage bunkers 13. By means of proportioningdevices which are not shown in greater detail the raw materialcomponents are extracted individually or jointly and ground to raw mealin a grinding apparatus 14.

An analysing means 15 for analysis of the the mineralogical and/orchemical composition of the raw material components can be providedbefore the grinding apparatus 14. Alternatively after the grindingapparatus 14 a further analysing means 16 can be provided, with the aidof which the mineralogical and/or chemical composition of the rawmeal/raw meal components can be determined.

The raw meal then proceeds to the raw meal silo installation 4 whichcomprises a plurality of raw meal silos 4 a to 4 h. The individual rawmeal silos can be constructed separately or as individual silocompartments are combined into multi-compartment silos. The plurality ofraw meal silos offers the possibility of filling them with raw meal ofdifferent mineralogical and/or chemical composition. In this caseindividual raw material components 12 a to 12 e can at least bepartially separately ground and stored in separate raw meal silos. Inpractice several raw material components can be advantageously groundjointly and other raw material components can be ground separately andstored in the raw meal silos. Naturally the possibility also exists ofgrinding various components with different quantitative ratios togetherand storing them. By means of the analysis device 16 it is possible atany time to have an idea of the composition of the material and theappropriate raw meal silo can be controlled in a targeted manner.

In the next process section the raw meal is burned to clinker. Theprocess section “clinker burning” usually comprises a preheater 21, acalciner 22, a rotary kiln 20 as well as a clinker cooler 23. The rawmeal is extracted by targeted extraction from one or a plurality of rawmeal silos 4 a to 4 h in the desired composition and transporteddirectly to the combustion plant 2. Thus the raw meal extracted from theraw meal silo is not only stored temporarily in collecting silo. In thecombustion plant it is preheated in the preheater in counterflow to theexhaust gases from the rotary kiln, precalcined in the calciner andfinally burned to clinker in the rotary kiln. The cooling then takesplace in the clinker cooller 23 disposed downstream.

In an analysing means 24 the mineralogical and/or chemical compositionof the raw meal extracted from the raw meal silos is determined. In afurther sampling and analysing means 25 disposed in or after the clinkercooler 23 the mineralogical and/or chemical composition of the clinkeris finally determined. In this case the samples can be separated intofractions according to density and grain size.

The burned clinker is delivered to the clinker silo installation 5 whichalso comprises a plurality of clinker silos 5 a to 5 g. Here too it isagain possible for the filling of the individual clinker silos and theextraction of the clinker from one or a plurality of clinker silos to beregulated as a function of the desired mineralogical and/or chemicalcomposition of the cement to be produced. An analysing means 26determines the mineralogical and/or chemical composition of the clinkerextracted from the clinker silos.

The finished cement comprises in addition to the clinker gypsum andfurther additives which are ground together in the cement grindinginstallation 3 in a mill 30. In order to ensure a uniform material flowto the mill 30, feed bins 31 (additives), 32 (gypsum) and 33 (clinker)are provided. The individual components are extracted by way ofproportioning devices (which are not shown in greater detail) acordingto the desired composition and delivered directly to the cement grindinginstallation 3. Finally the ground cement enters the cement silo 6 andfrom there can be filled into suitable transport means.

Instead of an individual clinker feed bin 33 the various qualities ofclinker can also be stored in a plurality of clinker feed bins andtransported from there together with the other components to the mill.The analysing means 26 can then also be disposed between the feed binsand the mill 30.

The raw meal silo installation 4 is described in greater detail belowwith reference to FIG. 2. However, the following description alsoapplies to the clinker silo installation 5. In order to avoidunnecessary repetitions, therefore, reference is made below basically tothe raw meal silo installation 4. The reference numerals in connectionwith the clinker silo installation 5 are additionally given after theoblique stroke.

The first process, in this case the preparation of the raw material, isidentified by the reference numerals 1/2. The subsequent process, inthis case the clinker burning, is identified by the reference numerals2/3. The mineralogical and/or chemical composition of the raw mealand/or raw meal components ground during the preparation of the rawmaterial 1 is analysed by the analysing means 16/25. The result of theanalysis is communicated to a control means 7 which controls materialdiverters 40 in order to establish the filling of one specific or aplurality of raw meal silos/clinker silos. The control means 7 alsomonitors the filling level of each individual raw material silo/clinkersilo by means of sensors 41.

Each of the raw material silos has an appertaining outlet proportioningdevice 42 which can be controlled in a targeted manner by way of thecontrol means 7. In this way können one or a plurality of outletproportioning devices 42 can be controlled in a targeted manner in orderto deliver a stream of raw meal with a desired mineralogical and/orchemical composition to the subsequent clinker burning process. The rawmeal composition is determined by the analysing means 25/26 ermitteltand used if need be for correction and/or adjustment of the outletproportioning devices 42.

The plurality of raw meal silos or clinker silos increaes theflexibility in the material composition. Therefore it is also possisbleto effect a corresponding correction of the raw meal composition duringclinker burning in a very short time, for example when other fuels areused. It is also possible to carry out the most rapid possible change inthe raw meal composition by the analysis of the burned clinker.Furthermore, fluctuations in the clinker composition can be compensatedfor by targeted mixing of clinker from two or more clinker silos.

During combined grinding an unwanted chemical composition which isseparated according to grain sizes is frequently observed. However, withthe bove installation it is possible to produce individual raw materialcomponents by separate grinding and storage. Bringing togetherseparately ground raw material components ensures a better control ofthe chemical composition irrespective of the grindability. Alsocorrective components which are distinguished by a high concentration ofa pricipal oxide or of a subsidiary component can be easily produced andstored separately for later corrections and and if need be can be addedto the mixture with short dead times.

It is known that the cement clinker has a concentration of the clinkerphases which differs according to grain size. It may therefore beprovided that for the determination of the mineralogical and/or chemicalcomposition of the raw meauclinker the analysing means take sampleswhich are fractionated according to grain size and/or density. It isalso conceivable that the filling of the raw meal silo/clinker siloaccording to grain size and/or density is effected by fractionation bymeans of screening or sifting. Thus in particular individual diverters40 can be provided with suitable means for screening or sifting.

1. Method and apparatus for the production of a hydraulic binding agentfrom a plurality of raw material components (12 a to 12 e), wherein theraw material components are ground to a raw meal, the raw meal is burnedto clinker in a combustion plant (2) and finally the clinker is groundtogether with further inter-grinding materials, characterised in thatthe mineralogical and/or chemical composition of the raw meal and/or theclinker is analysed, at least two separate raw meal silos/clinker silos(4 a to 4 h, 5 a to 5 g) are provided in each case for the raw mealand/or the clinker and are filled with raw meal/clinker of differentmineralogical and/or chemical composition, and the composition of theraw meal to be burned and/or of the clinker to be ground is fixed bycontrolled extraction as a function of the analysed composition of theraw meal/clinker from one or a plurality of raw meal silos/clinkersilos.
 2. Method as claimed in claim 1, characterised in that themineralogical and/or chemical composition of the clinker is determinedand used for control of the extraction of the raw meal from the raw mealsilo (4 a-4 h).
 3. Method as claimed in claim 1, characterised in thatindividual raw material components are at least partially groundseparately and stored in separate raw meal silos (4 a-4 h).
 4. Method asclaimed in claim 1, characterised in that the filling of the clinkersilos and the extraction of the clinker from one or a plurality ofclinker silos (5 a to 5 g) are regulated as a function of the desiredmineralogical and/or chemical composition of the cement to be created.5. Method as claimed in one or more of the preceding claims,characterised in that for determination of the mineralogical and/orchemical composition of the raw meal/clinker samples which arefractionated according to grain size and/or density samples can be takenand analysed.
 6. Method as claimed in one or more of the precedingclaims, characterised in that the filling of the raw meal silos/clinkersilos (4 a to 4 h) (5 a to 5 g) is carried out by fractionation by meansof screening or sifting according to grain size and/or density. 7.Method as claimed in one or more of the preceding claims, characterisedin that the raw meal to be burned and/or the clinker to be ground isdelivered directly to the combustion plant/a cement grindinginstallation after the controlled extraction frm one or a plurality ofraw meal silos/clinker silos.
 8. Apparatus for the production of ahydraulic binding agent from a plurality of raw material components witha grinding apparatus (14) for grinding of the raw material components toraw meal, with a combustion plant (2) for burning of the raw meal toclinker and a cement grinding installation (3) for grinding of theclinker, characterised by at least one analysing means (16, 24, 25, 26)for analysis of the mineralogical and/or chemical composition of the rawmeal and/or of the clinker, a raw meal silo installation and/or aclinker silo installation (4, 5), wherein at least two separate raw mealsilos/clinker silos are provided in each case for the raw meal and/orthe clinker, a raw meal silo installation and/or a clinker siloinstallation (4, 5), wherein at least two separate raw mealsilos/clinker silos are provided in each cas for the raw meal and/or theclinker, and a control device for filling of the raw meal silo/clinkersilo (4 a to 4 h, 5 a to 5 g) as a function of the mineralogical and/orchemical composition of the raw meal/clinker and for fixing thecomposition of the raw meal to be burned and/or of the clinker to beground by controlled extraction as a function of the analysedcomposition of the raw meal/clinker from one or a plurality of raw mealsilos/clinker silos (4 a to 4 h, 5 a to 5 g).